water temp sensor - sleep() does not work as intended!!

[Ricardosgeral]

I have a water temp sensor DS18B20 (https://www.adafruit.com/product/381) It's connected to pin GPIO4 and it has a 10k resistor like recommended I want to have readings every second So I've done this

from time import sleep
from datetime import datetime
from w1thermsensor import W1ThermSensor
## Constants
MEASURE_INTERVAL = 1   #seconds
while True:
    d = datetime.now()
    time_ = '{:%H:%M:%S}'.format(d)
    # (DS18B) Water temperature sensor
    try:
        w = W1ThermSensor()
        water_temp = str(w.get_temperature())  # default pin GPIO4 for data and temp in Celsius degrees
    except:
        water_temp = '0'
    print(time_,water_temp)
    sleep(MEASURE_INTERVAL)

However instead 1 sec interval I'm having 2 sec consistently (most of times) this is the result

17:20:55 19.437
17:20:57 19.437
17:20:59 19.437
17:21:01 19.437
17:21:03 19.437
17:21:05 19.437
17:21:06 19.437
17:21:08 19.437
17:21:10 19.437
17:21:12 19.437
17:21:14 19.437
17:21:16 19.437
17:21:17 19.437
17:21:19 19.437
17:21:21 19.437

Why? I don't understand should i change something in W1ThermSensor class?

[bsimmo]

It takes about 1 second for the sensor to start, take, calculate and give it's reading. (~750ms normally). It is not an instant reading and your program will stop until the reading has been given. Hence getting close to a 2second interval.

On 2 Feb 2018 18:09, "Ricardosgeral" notifications@github.com wrote:

I have a water temp sensor DS18B20 (https://www.adafruit.com/product/381) It's connected to pin GPIO4 and it has a 10k resistor like recommended I want to have readings every second So I've done this `from time import sleep from datetime import datetime from w1thermsensor import W1ThermSensor Constants

MEASURE_INTERVAL = 1 #seconds

while True: d = datetime.now() time_ = '{:%H:%M:%S}'.format(d)

(DS18B) Water temperature sensor

try: w = W1ThermSensor() water_temp = str(w.get_temperature()) # default pin GPIO4 for data and temp in Celsius degrees except: watertemp = '0' print(time,water_temp)

sleep(MEASURE_INTERVAL)`

However instead 1 sec interval I'm having 2 sec consistently (most of times) this is the result

17:20:55 19.437 17:20:57 19.437 17:20:59 19.437 17:21:01 19.437 17:21:03 19.437 17:21:05 19.437 17:21:06 19.437 17:21:08 19.437 17:21:10 19.437 17:21:12 19.437 17:21:14 19.437 17:21:16 19.437 17:21:17 19.437 17:21:19 19.437 17:21:21 19.437

Why? I don't understand should i change something in W1ThermSensor class?

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[bsimmo]

And the 'mostly 2 seconds' is due to ~1.75 seconds being added up and eventually the rounding will look like 1 second instead of two second. Add in milliseconds and you should see.

[Ricardosgeral]

Ok thanks! SO my best option is to define

EFFECTIVE_INTERVAL = 1 #seconds MEASURE_INTERVAL = EFFECTIVE_INTERVAL - 0.800 # to account with the delay of the sensor

this way it works 90% of times

[timofurrer]

Thanks @bsimmo ! @Ricardosgeral does that solve your problem?

[Ricardosgeral]

Yes! But I placed the reading in a separate Thread. Thanks

On 5 Feb 2018 12:31 p.m., "Timo Furrer" notifications@github.com wrote:

Thanks @bsimmo https://github.com/bsimmo ! @Ricardosgeral https://github.com/ricardosgeral does that solve your problem?

— You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub https://github.com/timofurrer/w1thermsensor/issues/45#issuecomment-363071319, or mute the thread https://github.com/notifications/unsubscribe-auth/AdESUDjeDe8g-02h3qqxNKEZr2biwAmeks5tRvSTgaJpZM4R3h1z .